Laser Voltage Probing (LVP) is an optical tool for failure analysis and real time characterization and/or logic debugging of electrical signals propagating at operational speeds through an integrated circuit (IC). Conventional LVP systems rely on free carrier index changes and free carrier absorption within semiconductors. Infrared wavelengths are used to take advantage of silicon's relative transparency for backside probing. The incident light is reflected back, captured, detected, and amplified. The small modulations in reflected light intensity resulting from carrier density changes with electric field are utilized to determine local transistor logic states as a function of time.
With the continual reduction of IC feature sizes (e.g., a trace, a transistor, a CMOS transistor, a diode, a PN junction or other semiconductor component or device that transfers or conveys free carriers or conducting current, etc.), backside, laser-based failure analysis tools are limited in spatial resolution by the refraction limits of infrared light and the relatively long wavelengths required for through-silicon probing. Even with state of the art solid immersion lenses (SILs), modern 22 nanometer (nm) devices are at and past the limit of practical resolution for LVP systems utilizing infrared light.